Ultrasonic diagnostic equipment has become an indispensable tool for clinical use. For approximately the past twenty years, real-time B-mode ultrasound imagers are used for investigating all soft tissue structures in the human body. One of the recent developments within medical imaging technology is the development of Doppler ultrasound scanners. Doppler ultrasound is an important technique for non-invasively detecting and measuring the velocity of moving structures, and particularly to display an estimate of blood velocity in the body in real time.
The basis of Doppler ultrasonography is the fact that reflected and/or scattered ultrasonic waves from a moving interface undergoes a frequency shift. In general the magnitude and the direction of this shift provides information regarding the motion of this interface. How much the frequency is changed depends upon how fast the object or moving interface is moving. Doppler ultrasound has been used mostly to measure the rate of blood flow through the heart and major arteries.
There are several forms of depiction of blood flow in medical Doppler imaging or more generally different velocity estimation systems that currently exist: Color Flow imaging, Power Doppler and Spectral sonogram. Color flow imaging (CFI), interrogates a whole region of the body, and displays a real-time image of mean velocity distribution. CFI provides an estimate of the mean velocity of flow within a vessel by color coding the information and displaying it, super positioned on a dynamic B-mode image or black and white image of anatomic structure. In order to differentiate flow direction, different colors are used to indicate velocity toward and away from the transducer.
While color flow imaging displays the mean or standard deviation of the velocity of reflectors, such as the blood cells in a given region, power Doppler (PD) displays a measurement of the amount of moving reflectors in the area, similarly to the B-mode image""s display of the total amount of reflectors. A power Doppler image is an energy image in which the energy of the flow signal is displayed. Thus, power Doppler depicts the amplitude or power of the Doppler signals rather than the frequency shift. This allows detection of a larger range of Doppler shifts and thus better visualization of small vessels. These images give no velocity information, but only show the direction of flow. In contrast, spectral Doppler or spectral sonogram utilizes a pulsed wave system to interrogate a single range gate or sampling volume, and displays the velocity distribution as a function of time. The sonogram can be combined with the B-mode image to yield a duplex image. Typically, the top side displays a B-mode image of the region under investigation, and the bottom displays the sonogram. Similarly, the sonogram can also be combined with the CFI or PD image to yield a triplex image. The time for data acquisition is then divided between acquiring all three sets of data, and the frame rate of the images is typically decreased, compared to either CFI or duplex imaging.
The current ultrasound systems require extensive complex data processing circuitry in order to perform the imaging functions described herein. Doppler processing for providing two-dimensional depth and Doppler information in color flow images, power Doppler images and/or spectral sonograms require millions of operations per second. There exists a need for an ultrasound imaging system that provides for compute-intensive systems and methods to efficiently address the data processing needs of information, such as Doppler processing.
The present invention is directed to an ultrasound imaging system and method for Doppler processing of data. The ultrasonic imaging system efficiently addresses the data computational and processing needs of Doppler processing. Software executable sequences in accordance with a preferred embodiment of the present invention determines the phase shift and the auto-correlation phase of filtered image data. In a preferred embodiment, the system of ultrasonic imaging also includes a sequence of instructions for Doppler processing that provides the functions for demodulation, Gaussian Match filtering, auto-correlation calculation, phase shift calculation, frame averaging, and scan conversion.
In a preferred embodiment, the processing system includes parallel processing elements which execute Single Instruction Multiple Data (SIMD) or Multiple Instruction Multiple Data (MIMD) instructions. A computer having a Pentium(copyright) III processor including MMX(trademark) technology is an exemplary computational device of a preferred embodiment of the ultrasonic imaging system in accordance with the present invention.
A method of the present invention includes imaging a region of interest with ultrasound energy using a portable ultrasound imaging system which in turn includes a transducer array within a handheld probe. An interface unit is connected to the handheld probe with a cable interface. The interface unit has a beamforming device connected to a data processing system with another cable interface. Output signals from the interface unit are provided to the handheld probe to actuate the transducer array, which in turn delivers ultrasound energy to the region of interest. The ultrasound energy returning to the transducer array is collected from the region of interest and transmitted from the handheld probe to the interface unit. A beamforming operation is performed with the beamforming device in the interface unit. The method further includes transmitting data from the interface unit to the data processing system such that the data processing system receives a beamformed electronic representation of the region of interest. The data processing system has at least one parallel processing element integrated with a microprocessor to execute a sequence of instructions for Doppler processing and displaying of Doppler images.
In a preferred embodiment, the ultrasound imaging system of the present invention includes a processing module; and memory operably coupled to the processing module, wherein the memory stores operational instructions that cause the processing module to map serial data to a vector representation, demodulate the data to obtain in-phase and quadrature sample data, calculate an auto-correlation function of the data, calculate a phase shift of the auto-correlation function represented as a monotonic function in the interval corresponding to the range of Doppler velocities according to the Nyquist criterion and expressed as a simple mathematical function, convert the phase shift to an index and display the images, for example, as color images.
The foregoing and other features and advantages of the system and method for ultrasound imaging will be apparent from the following more particular description of preferred embodiments of the system and method as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views.